1. Field of the Invention
The present invention relates to a digital signal recording apparatus for recording digital coded signals on a solid-state memory and a digital signal reproducing apparatus.
2. Description of the Related Art
Digital signal recording and reproducing apparatus using solid-state memories as recording media, as compared with those apparatus using the more conventional recording media such as magnetic tapes, magnetic disks, and optical disks, are resistant to vibrations and other types of shock and exhibit excellent characteristics such as high speed and low power consumption. Such digital signal recording and reproducing apparatus hold great promise as the next-generation recording and reproducing apparatus. However, the per-byte-cost of solid-state memories is extremely high as compared with other recording media, and this high cost has been a major factor blocking the practical realization of digital signal recording and reproducing apparatus capable of achieving long recording/reproduction times.
Signal compression techniques provide an effective means of increasing the utilization of solid-state memories and help to realize the practical utilization of digital recording and reproducing apparatus. However, the difficulty is that simply increasing the compression ratio will in turn result in recording quality degradation. In view of this difficulty, there have been proposed various methods aimed at increasing the amount of information that can be recorded while minimizing the degradation of recording quality. Among them, Japanese Laid-Open Patent Publication No. 2-305053, which is the prior art closest to the present invention, discloses the following method.
According to this prior art method, when there is a sufficient memory capacity, digital signals are encoded at a high bit rate and recorded on a solid-state memory. When the remaining capacity of the solid-state memory gets low, the data previously recorded at the high bit rate are read out of the solid-state memory and re-encoded at a lower bit rate, using a different compression algorithm than that for the previous recording, the re-encoded data then being stored into the solid-state memory. This series of operations is repeated to create free space in the solid-state memory. By varying the encoding bit rate in this manner, an increased amount of information can be recorded while minimizing the degradation in recording quality.
However, in order to create free space in the solid-state memory, the data previously recorded at the high bit rate have to be read out of the solid-state memory and re-encoded at a lower bit rate using a lower-bit-rate compression algorithm different from that for the previous recording. This increases the hardware load and decreases the efficiency. The prior art method has had a further problem that depending on the amount of data, unused space may be left in the solid-state memory, lowering the utilization of the solid-state memory.